EP1202561B1 - Apparatus and method for reading out several sets of pixels with different sampling rates - Google Patents

Apparatus and method for reading out several sets of pixels with different sampling rates Download PDF

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Publication number
EP1202561B1
EP1202561B1 EP01125777A EP01125777A EP1202561B1 EP 1202561 B1 EP1202561 B1 EP 1202561B1 EP 01125777 A EP01125777 A EP 01125777A EP 01125777 A EP01125777 A EP 01125777A EP 1202561 B1 EP1202561 B1 EP 1202561B1
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European Patent Office
Prior art keywords
picture elements
groups
pixels
read out
image
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EP01125777A
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German (de)
French (fr)
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EP1202561A3 (en
EP1202561A2 (en
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Norbert Dr.-Ing Jung
Kai Eck
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Philips Intellectual Property and Standards GmbH
Koninklijke Philips NV
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Philips Intellectual Property and Standards GmbH
Koninklijke Philips Electronics NV
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N3/00—Scanning details of television systems; Combination thereof with generation of supply voltages
    • H04N3/10—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical
    • H04N3/14—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical by means of electrically scanned solid-state devices
    • H04N3/15—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical by means of electrically scanned solid-state devices for picture signal generation
    • H04N3/155—Control of the image-sensor operation, e.g. image processing within the image-sensor
    • H04N3/1562—Control of the image-sensor operation, e.g. image processing within the image-sensor for selective scanning, e.g. windowing, zooming
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/40—Extracting pixel data from image sensors by controlling scanning circuits, e.g. by modifying the number of pixels sampled or to be sampled
    • H04N25/44—Extracting pixel data from image sensors by controlling scanning circuits, e.g. by modifying the number of pixels sampled or to be sampled by partially reading an SSIS array
    • H04N25/443—Extracting pixel data from image sensors by controlling scanning circuits, e.g. by modifying the number of pixels sampled or to be sampled by partially reading an SSIS array by reading pixels from selected 2D regions of the array, e.g. for windowing or digital zooming
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/40—Extracting pixel data from image sensors by controlling scanning circuits, e.g. by modifying the number of pixels sampled or to be sampled
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/70—SSIS architectures; Circuits associated therewith
    • H04N25/76—Addressed sensors, e.g. MOS or CMOS sensors
    • H04N25/7795—Circuitry for generating timing or clock signals

Definitions

  • the invention relates to a method for reading out an image sensor subdivided electronic image sensor, from which pixels or Profpunkropathy can be read with a predetermined cycle time. Furthermore, the invention relates to a device for reading out a subdivided into pixels electronic image sensor, which contains an addressing unit for selecting the readable in a clock pixels and / or pixel groups and a reading unit for reading the selected and addressed pixels and / or pixel groups.
  • Electronic image sensors as used for example in the representation of X-ray images, usually consist of a two-dimensional array of pixels. These pixels are read out at a predetermined, highest possible sampling rate of typically 30 to 60 images per second readout units, to be subsequently processed by a computer and displayed on a monitor, among other things. As a rule, the pixels are divided into rows (or columns), and one complete row (or column) is read out per read-out cycle.
  • the DE19534334 describes a method for the optoelectronic scanning of originals, in particular in scanners, in which image signal values are read at different speeds from an optoelectronic transducer.
  • the template is divided into different sections, where sampled not sections of interest are discarded.
  • the EP-A-0644712 discloses an image acquisition system with a CCD sensor for an X-ray apparatus, similar to the DE19534334 Parts of the read-out image are discarded.
  • a method in which portions of a two-dimensional image sensor can be displayed zoomed.
  • an image of typically 1000 ⁇ 1000 physical pixels takes place on a smaller amount of, for example, 500 ⁇ 500 pixels shown, wherein for a magnification, a partial area of 500 ⁇ 500 physical pixels 1: 1 can be assigned to the pixels shown.
  • physical pixels are combined line by line and / or column by column in order to be able to image a larger number of such physical pixels onto the limited number of pixels shown.
  • the special feature of the method is that the handling of the combination of pixels varies locally, so that a non-integer factor between the number of physical pixels and the represented pixels can be achieved. While with such a method the spatial resolution in the representation of the image can be varied, the temporal resolution remains unchanged.
  • an object of the present invention is to provide an apparatus and a method with which a rapid representation of an electronically acquired image is achieved.
  • the method for reading an electronic image sensor subdivided into pixels is based on the fact that pixels or groups of pixels can be read out with a given cycle time.
  • the pixel groups may be Act picture lines.
  • the cycle time corresponds to the time required for the readout of a pixel or pixel group and is usually limited by the performance of the electronic components downwards.
  • the method is characterized in that at least two sets of pixels and / or pixel groups can be distinguished, the pixels and / or pixel groups of a first set being read out at a different sampling rate than the pixels and / or pixel groups of a second set. If there are n ⁇ 2 such sets, there are n different sample rates accordingly.
  • the image areas of interest are displayed in the best quality and temporally higher resolution method.
  • the near instant availability of images of the areas of interest also improves the interactive properties of the image processing kernels, which may be of particular importance in medical x-ray imaging techniques. For example, the time-critical placement of a catheter or needle in a patient's body is very important in that the executive doctor receives up-to-date pictures of the procedure.
  • the pixels of the Image sensor grouped in lines of a two-dimensional image surface, the lines are read out in each case uniformly with a certain cycle time.
  • Line-by-line reading of image sensors is widely used in the art and is especially used with FDXD detectors (FDXD stands for "Flat Dynamic X-Ray Detector", ie flat dynamic X-ray detector). Nevertheless, it may be possible for future detectors to address only parts of lines, so that the areas of interest and higher scanned areas (ROI) need not necessarily cover entire lines, but in principle may take any shape.
  • the different sets of pixels and / or pixel groups interlock at least in a portion of the image area.
  • the pixel lines of an image may be alternately associated with two or more sets of different sampling rates.
  • the even-numbered double-sampling-frequency image lines may be scanned like the odd-numbered image lines.
  • the even-numbered image lines thus provide a representation of the complete image with high temporal and reduced spatial resolution.
  • the odd-numbered lines read half as often then provide improved spatial resolution.
  • the ratio of the sampling rates in the two image line sets can be chosen arbitrarily.
  • the further processing of the signals of read-out pixels takes place as a function of the sampling rate of the respective pixel.
  • the signal gain can be adjusted according to the sampling rate.
  • charge accumulation takes place in the pixels, which increases steadily with the exposure time. Rarer scanned pixels therefore contain a correspondingly higher charge accumulated over a longer period of time.
  • the sensitivity of the readout devices is adjusted accordingly to this higher expected charge. It is important to ensure that in the less frequently read image areas, the sampling frequency is still high enough so that no saturation of the pixels occurs, which would result in a loss of information. This applies at least to those pixels which still contain information of interest. A possible saturation of, for example, outside the transmission range of a patient lying pixels is irrelevant.
  • the image sensor may be one that is sensitive to X-rays.
  • image sensors are used in medical imaging methods such as, for example, X-ray computed tomography, wherein in the corresponding applications often a high-temporal representation of spatially limited areas of interest is required.
  • the equipment required for medical imaging procedures are usually very costly, so that the optimal use of existing resources is particularly advantageous here.
  • those pixels and / or pixel groups which are read out at a lower sampling rate are irradiated with a lower intensity.
  • the pixels read out at a lower sampling rate have more time between two read-out clocks in order to accumulate image information, for example in the form of charge.
  • These pixels can thus be exposed with a lower intensity of the radiation used for image generation, without the image information available in the case of the less frequent scanning of the pixels being reduced as a result.
  • the thus given possibility of exposing image areas with a lower intensity is advantageous, in particular in the case of medical X-ray images, because in this case, the dose to which the patient is exposed can be minimized by a local beam attenuation.
  • the invention further relates to a device for reading an electronic image sensor subdivided into pixels, which contains an addressing unit for selecting the pixels and / or pixel groups to be read out in one clock and a reading unit for reading the selected and addressed pixels and / or pixel groups.
  • the addressing unit is set up such that it selects the addressed pixels and / or pixel groups at different rates.
  • the pixels or pixel groups in question are thus not selected in the same order with the same frequency, but there are at least two sets of pixels or pixel groups, the elements of which are selected by the addressing unit more often than the elements of the different amount.
  • the above-explained method can be implemented, so that the advantages described there can be achieved.
  • the addressing unit and the reading unit of the device can in particular be designed such that they can also realize the various variants of the method, ie for example a line-by-line division of the image, intermeshing pixel quantities of different sampling rates, a sensitivity of the image sensor for X-rays and the like.
  • the reading unit can be set up in such a way that it aligns the processing of the read-out signals of the pixels with the rate at which the respective pixels and / or pixel groups were addressed.
  • the signal gain is adjusted to this rate, so that it can be taken into account that less frequently sampled pixels expect a higher signal strength due to the longer exposure time.
  • FIG. 1 shows the X-ray image 1 of a hand, wherein in the center of the image, a region of interest 2 (ROI) is highlighted.
  • the rest 3 of the image represents a region of lesser interest.
  • the gate lines 5 of the region of interest 2 and the gate lines 6 of the remaining region 3 are indicated at the edge of the image, and the reinforcement chips 4 are shown at the lower edge of the image, which serve the reading out of picture lines.
  • the image sensor is an FDXD detector which is read out by transmitting line by line directly to a field output. It will be read out a line does not affect any lines of the neighborhood. Unlike CCD-based imagers, for example, complete readout of the image is not required every time.
  • the non-read-out picture lines which were not addressed in a particular cycle or cycle, as a rule, remain unimpaired for their further use. This is true on condition that no relevant pixel reaches saturation during the multiple exposures by X-ray pulses. Non-relevant pixels are, for example, those exposed to the direct beam without passage through the patient.
  • central ROI 2 is read out by addressing the corresponding gate lines 5 with an increased sampling rate.
  • This sampling rate may be, for example, 60 frames per second.
  • a lower rate of, for example, one-half or one-quarter of the maximum sampling rate (ie, 30 or 15 frames per second) then the complete image is read using all the gate lines 5 and 6 according to their order.
  • the sensitivity of the amplifying chips 4 is switched during readout according to the amount of charge expected inside and outside the ROI 2.
  • FIG. 2 schematically shows the time sequences of various processes in carrying out the method according to the invention.
  • the time is plotted on the horizontal axis.
  • the top diagram a) of FIG. 2 shows the exposure pulses emitted by the x-ray tube. During each pulse accumulates in the pixels of the image sensor additively a corresponding amount of charge, which is dissipated when reading the pixel.
  • the second diagram b) of FIG. 2 shows the addressing of the gate lines 5 and thus the reading of the area of interest 2 (ROI). After completion of the readout, a new X-ray pulse can be given. Since the complete image does not have to be read out between two such X-ray pulses, their distance can be correspondingly shortened, which leads to the improved temporal resolution of the representation of the region of interest 2.
  • the addressing of the gate lines 6 of the area 3 outside the ROI 2 is shown.
  • the region of interest ROI is read four times before the remaining area 3 of the image is read out once.
  • the ROI of interest is thus detected at a four times higher sampling rate than the rest of the image.
  • the interval between two X-ray pulses is read out the complete image, ie both the region of interest ROI and the remaining part 3 of the image. Accordingly, a longer time is required for the entire readout, so that the interval between the two X-ray pulses is to be selected correspondingly larger.
  • FIG. 2 shows the sensitivity of the amplifiers during readout. It can be seen that the sensitivity is high during the reading out of pixels of the region of interest ROI and lower during the reading out of the remaining image region 3. This change in sensitivity takes into account that the less frequently read image areas 3 were exposed several times between two reading processes (four times in the example shown), so that they allow a correspondingly higher charge quantity to be expected. This higher charge is compensated by the reduced sensitivity.
  • the method according to the invention thus makes it possible to represent the particularly interesting region ROI of a picture with a higher sampling rate and therefore in a better time-resolved manner. Less interesting image areas are less resolved in time, but show a better signal-to-noise ratio due to the longer exposure.

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  • Signal Processing (AREA)
  • Computer Vision & Pattern Recognition (AREA)
  • Apparatus For Radiation Diagnosis (AREA)
  • Measurement Of Radiation (AREA)
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Description

Die Erfindung betrifft ein Verfahren zum Auslesen eines in Bildpunkte unterteilten elektronischen Bildsensors, aus welchem mit einer vorgegebenen Taktdauer Bildpunkte oder Bildpunkrgruppen ausgelesen werden können. Ferner betrifft die Erfindung eine Vorrichtung zum Auslesen eines in Bildpunkte unterteilten elektronischen Bildsensors, welche eine Adressierungseinheit zur Auswahl der in einem Takt auszulesenden Bildpunkte und/oder Bildpunktgruppen sowie eine Leseeinheit zum Auslesen der ausgewählten und adressierten Bildpunkte und/oder Bildpunktgruppen enthält.The invention relates to a method for reading out an image sensor subdivided electronic image sensor, from which pixels or Bildpunkrgruppen can be read with a predetermined cycle time. Furthermore, the invention relates to a device for reading out a subdivided into pixels electronic image sensor, which contains an addressing unit for selecting the readable in a clock pixels and / or pixel groups and a reading unit for reading the selected and addressed pixels and / or pixel groups.

Elektronische Bildsensoren, wie sie zum Beispiel bei der Darstellung von Röntgenbildern verwendet werden, bestehen in der Regel aus einem zweidimensionalen Feld ("array") von Bildpunkten. Diese Bildpunkte werden mit einer vorgegebenen, möglichst hohen Abtastrate von typischerweise 30 bis 60 Bildern pro Sekunde von Ausleseeinheiten ausgelesen, um anschließend von einem Computer weiterverarbeitet und unter anderem auf einem Monitor dargestellt zu werden. In der Regel sind die Bildpunkte dabei in Zeilen (oder Spalten) eingeteilt, und pro Auslesetakt wird jeweils eine komplette Zeile (oder Spalte) ausgelesen.Electronic image sensors, as used for example in the representation of X-ray images, usually consist of a two-dimensional array of pixels. These pixels are read out at a predetermined, highest possible sampling rate of typically 30 to 60 images per second readout units, to be subsequently processed by a computer and displayed on a monitor, among other things. As a rule, the pixels are divided into rows (or columns), and one complete row (or column) is read out per read-out cycle.

Wenn nur ein Teilbereich des zweidimensionalen Bildsensors von Interesse ist, ist es bekannt, das Auslesen auf die in diesem Teilbereich liegenden Bildpunkte beziehungsweise Zeilen zu beschränken- Hierdurch kann erreicht werden, dass die in dem interessierenden Bereich liegenden Bildpunkte mit einer höheren Abtastrate ausgelesen werden können, da sie bei gleichbleibender Dauer eines einzelnen Auslesetaktes für einen Bildpunkt bzw. eine Zeile öfter an die Reihe kommen.If only a subarea of the two-dimensional image sensor is of interest, it is known to restrict the readout to the pixels or lines lying in this subarea. In this way it can be achieved that the pixels located in the region of interest can be read out at a higher scanning rate, because they come more often for a pixel or a line with the same duration of a single read-out clock.

Die DE19534334 beschreibt ein Verfahren zur optoelektronischen Abtastung von Vorlagen, insbesondere bei Scannern, bei der Bildsignalwerte mit verschiedenen Geschwindigkeiten aus einem optoelektronischen Wandler ausgelesen werden. Die Vorlage wird in verschiedene Abschnitte unterteilt, wobei abgetastete nicht interessierende Abschnitte verworfen werden.The DE19534334 describes a method for the optoelectronic scanning of originals, in particular in scanners, in which image signal values are read at different speeds from an optoelectronic transducer. The template is divided into different sections, where sampled not sections of interest are discarded.

Die EP-A-0644712 offenbart ein Bilderfassungssystem mit einem CCD Sensor für einen Röntgenapparat, bei dem ähnlich zur DE19534334 Teile des ausgelesenen Bildes verworfen werden.The EP-A-0644712 discloses an image acquisition system with a CCD sensor for an X-ray apparatus, similar to the DE19534334 Parts of the read-out image are discarded.

Des weiteren ist aus der DE 195 31 627 C1 ein Verfahren bekannt, bei dem Teilbereiche eines zweidimensionalen Bildsensors gezoomt dargestellt werden können. Bei diesem Verfahren findet eine Abbildung von typischerweise 1000 x 1000 physikalischen Bildpunkten auf eine kleinere Menge von zum Beispiel 500 x 500 dargestellten Bildpunkte statt, wobei für eine Vergrößerung ein Teilbereich von 500 x 500 physikalischen Bildpunkten 1 : 1 den dargestellten Bildpunkten zugeordnet werden kann. Für eine verkleinerte Darstellung werden dagegen physikalische Bildpunkte zeilenweise und/oder spaltenweise zusammengefasst, um eine größere Anzahl solcher physikalischer Bildpunkte auf die begrenzte Anzahl der dargestellten Bildpunkte abbilden zu können. Das Besondere des Verfahrens liegt darin, dass der Umgang der Zusammenfassung von Bildpunkte lokal variiert, so dass ein nichtganzzahliger Faktor zwischen der Anzahl der physikalischen und der dargestellten Bildpunkte erreicht werden kann. Während mit einem derartigen Verfahren die räumliche Auflösung bei der Darstellung des Bildes variiert werden kann, bleibt die zeitliche Auflösung unverändert.Furthermore, from the DE 195 31 627 C1 a method is known in which portions of a two-dimensional image sensor can be displayed zoomed. In this method, an image of typically 1000 × 1000 physical pixels takes place on a smaller amount of, for example, 500 × 500 pixels shown, wherein for a magnification, a partial area of 500 × 500 physical pixels 1: 1 can be assigned to the pixels shown. For a reduced representation, on the other hand, physical pixels are combined line by line and / or column by column in order to be able to image a larger number of such physical pixels onto the limited number of pixels shown. The special feature of the method is that the handling of the combination of pixels varies locally, so that a non-integer factor between the number of physical pixels and the represented pixels can be achieved. While with such a method the spatial resolution in the representation of the image can be varied, the temporal resolution remains unchanged.

Vor diesem Hintergrund ist Aufgabe der vorliegenden Erfindung, eine Vorrichtung und ein Verfahren zur Verfügung zu stellen, mit welchen eine schnelle Darstellung eines elektronisch erfassten Bildes erreicht wird.Against this background, an object of the present invention is to provide an apparatus and a method with which a rapid representation of an electronically acquired image is achieved.

Diese Aufgabe wird durch ein Verfahren mit den Merkmalen des Anspruchs 1 und eine Vorrichtung mit den Merkmalen des Anspruchs 7 gelöst. Vorteilhafte Ausgestaltungen sind in den Unteransprüchen entfalten.This object is achieved by a method having the features of claim 1 and an apparatus having the features of claim 7. Advantageous embodiments are disclosed in the subclaims.

Das Verfahren zum Auslesen eines in Bildpunkte unterteilten elektronischen Bildsensors beruht darauf, dass Bildpunkte oder Bildpunktgruppen mit einer gegebenen Taktdauer ausgelesen werden können- Bei den Bildpunktgruppen kann es sich zum Beispiel um Bildzeilen handeln. Die Taktdauer entspricht der für das Auslesen eines Bildpunktes oder einer Bildpunktgruppe benötigten Zeit und wird in der Regel durch die Leistungsfähigkeit der elektronischen Bauelemente nach unten hin begrenzt. Das Verfahren ist dadurch gekennzeichnet, dass sich mindestens zwei Mengen von Bildpunkten und/oder Bildpunktgruppen unterscheiden lassen, wobei die Bildpunkte und/oder Bildpunktgruppen einer ersten Menge mit einer anderen Abtastrate als die Bildpunkte und/oder Bildpunktgruppen einer zweiten Menge ausgelesen werden. Wenn n ≥ 2 solche Mengen vorhanden sind, gibt es dementsprechend n verschiedene Abtastraten.The method for reading an electronic image sensor subdivided into pixels is based on the fact that pixels or groups of pixels can be read out with a given cycle time. For example, the pixel groups may be Act picture lines. The cycle time corresponds to the time required for the readout of a pixel or pixel group and is usually limited by the performance of the electronic components downwards. The method is characterized in that at least two sets of pixels and / or pixel groups can be distinguished, the pixels and / or pixel groups of a first set being read out at a different sampling rate than the pixels and / or pixel groups of a second set. If there are n ≥ 2 such sets, there are n different sample rates accordingly.

Durch das Verfahren werden somit in der Bildfläche verschiedene Bereiche geschaffen, welche jeweils mit unterschiedlicher Abtastrate ausgelesen werden. Dabei kann die Einteilung so stattfinden, dass ein besonders interessierender Bereich des Bildes ("region ofinterest" ROI) mit höherer Abtastrate ausgelesen wird als die übrigen Bildbereiche. Dies erlaubt dem Benutzer eine flexible Anpassung der Bildverarbeitungskette an die jeweiligen Anforderungen der aktuellen Anwendung, wobei gleichzeitig von den verfügbaren Ressourcen der Ausleseelektronik, der Datenübertragung und der Bildverarbeitung optimaler Gebrauch gemacht wird.As a result of the method, different areas are created in the image area, which are each read out with a different sampling rate. The division can take place in such a way that a particularly interesting region of the image ("region ofinterest" ROI) is read at a higher sampling rate than the remaining image regions. This allows the user to flexibly adapt the image processing chain to the particular needs of the current application, while optimally utilizing the available resources of the read-out electronics, data transmission and image processing.

Die interessierenden Bildbereiche werden bei dem Verfahren mit bester Qualität und zeitlich höher aufgelöst dargestellt. Die quasi sofortige Verfügbarkeit von Bildern der interessierenden Bereiche verbessert auch die interaktiven Eigenschaften der Bildverarbeitungskerte, was insbesondere bei medizinischen Röntgen-Bildgebungsverfahren von großer Bedeutung sein kann So kommt es zum Beispiel bei der zeitkritischen Plazierung eines Katheters oder einer Nadel im Körper eines Patienten sehr darauf an, dass der ausführende Arzt aktuelle Bilder des Vorgangs erhält.The image areas of interest are displayed in the best quality and temporally higher resolution method. The near instant availability of images of the areas of interest also improves the interactive properties of the image processing kernels, which may be of particular importance in medical x-ray imaging techniques. For example, the time-critical placement of a catheter or needle in a patient's body is very important in that the executive doctor receives up-to-date pictures of the procedure.

Bis auf die feine zeitliche Auflösung geht bei dem Verfahren aus den seltener abgetasteten Bildbereichen keine Information verloren, da die Bildinformation dort über mehrere Aufnahmen hinweg - zum Beispiel als Ladung - für das spätere Auslesen angesammelt wird. Eine solche längere Integration der Belichtung in den genannten Bereichen hat dort gleichzeitig ein verbessertes Signal-zu-Rauschen Verhältnis und damit eine qualitativ bessere Abbildung zur Folge. Typischerweise sind die Bildpunkte des Bildsensors in Zeilen einer zweidimensionalen Bildfläche gruppiert, wobei die Zeilen jeweils einheitlich mit einer bestimmten Taktdauer ausgelesen werden. Das zeilenweise Auslesen von Bildsensoren ist weitverbreiteter Stand der Technik und findet insbesondere bei den FDXD-Detektoren statt (FDXD ist die Abkürzung für "Flat Dynamic X-Ray Detector", d.h. flacher dynamischer Röntgendetektor). Dessen ungeachtet kann es jedoch gerade bei zukünftigen Detektoren möglich sein, nur Teile von Zeilen zu adressieren, so dass die interessierenden und höher abgetasteten Bereiche (ROI) nicht notwendigerweise ganze Zeilen abdecken müssen, sondern prinzipiell jede beliebige Form annehmen können.Except for the fine temporal resolution, no information is lost in the process from the less frequently sampled image areas since the image information is accumulated there over several recordings - for example as a charge - for later readout. Such a longer integration of the exposure in the areas mentioned at the same time there has an improved signal-to-noise ratio and thus a better quality picture result. Typically, the pixels of the Image sensor grouped in lines of a two-dimensional image surface, the lines are read out in each case uniformly with a certain cycle time. Line-by-line reading of image sensors is widely used in the art and is especially used with FDXD detectors (FDXD stands for "Flat Dynamic X-Ray Detector", ie flat dynamic X-ray detector). Nevertheless, it may be possible for future detectors to address only parts of lines, so that the areas of interest and higher scanned areas (ROI) need not necessarily cover entire lines, but in principle may take any shape.

Gemäß des Verfahrens greifen die verschiedenen Mengen der Bildpunkte und/oder Bildpunktgruppen (z.B. Zeilen) zumindest in einem Teilbereich der Bildfläche ineinander. Dies bedeutet Folgendes für die Mengen, die keine gemeinsamen Elemente haben: Wird zu den in den Mengen enthaltenen Bildpunkten in der Fläche des Bildsensors jeweils die konvexe Hülle gebildet, so überlappen sich diese konvexen Hüllen. Ein Teilbereich, in dem die Mengen ineinandergreifen, wird somit teilweise mit höherer und teilweise mit niedrigerer Abtastfrequenz dargestellt.According to the method, the different sets of pixels and / or pixel groups (e.g., lines) interlock at least in a portion of the image area. This means the following for the quantities which have no common elements: If the convex hull is formed in each case in the area of the image sensor for the pixels contained in the sets, then these convex hulls overlap. A partial area in which the quantities intermesh is thus shown partly with higher and partly with lower sampling frequency.

Insbesondere können die Bildpunktzeilen eines Bildes alternierend zwei oder mehr Mengen verschiedener Abtastraten zugeordnet sein. Zum Beispiel können die geradzahligen Bildzeilen mit doppelter Abtastfrequenz wie die ungeradzahligen Bildzeilen abgetastet werden. Die geradzahligen Bildzeilen bieten somit eine Darstellung des kompletten Bildes mit hoher zeitlicher und verringerter räumlicher Auflösung. Die nur halb so oft ausgelesenen ungeradzahligen Zeilen liefern dann eine verbesserte räumliche Auflösung nach. Selbstverständlich kann das Verhältnis der Abtastraten in den beiden Bildzeilen-Mengen beliebig gewählt werden. Ferner muss nicht nach jeder Bildzeile ein Wechsel der Abtastfrequenz erfolgen, sondern es können zum Beispiel drei benachbarte Zeilen mit geringerer Abtastfrequenz gefolgt von einer Zeile höherer Abtastfrequenz vorgesehen sein, wobei sich dieses Muster periodisch wiederholen kann oder auch nicht.In particular, the pixel lines of an image may be alternately associated with two or more sets of different sampling rates. For example, the even-numbered double-sampling-frequency image lines may be scanned like the odd-numbered image lines. The even-numbered image lines thus provide a representation of the complete image with high temporal and reduced spatial resolution. The odd-numbered lines read half as often then provide improved spatial resolution. Of course, the ratio of the sampling rates in the two image line sets can be chosen arbitrarily. Furthermore, it is not necessary to change the sampling frequency after every image line, but instead, for example, three adjacent lines with a lower sampling frequency followed by a line with a higher sampling frequency may or may not be repeated periodically.

Gemäß einer Weiterbildung des Verfahrens erfolgt die Weiterverarbeitung der Signale von ausgelesenen Bildpunkten in Abhängigkeit von der Abtastrate des jeweiligen Bildpunktes. Insbesondere kann die Signalverstärkung entsprechend der Abtastrate eingestellt werden. Hierdurch kann berücksichtigt werden, dass bei üblichen elektronischen Bildsensoren eine Ladungsansammlung in den Bildpunkten stattfindet, die stetig mit der Belichtungszeit steigt. Seltener abgetastete Bildpunkte enthalten daher eine entsprechend höhere, da über einen längeren Zeitraum angesammelte Ladung. Dieser höheren zu erwartenden Ladung wird die Sensitivität der Ausleseeinrichtungen entsprechend angepasst. Dabei ist darauf zu achten, dass in den seltener ausgelesenen Bildbereichen die Abtastfrequenz immer noch hoch genug liegt, so dass keine Sättigung der Bildpunkte auftritt, die einen Informationsverlust zur Folge hätte. Dies gilt zumindest für jene Bildpunkte, welche noch interessierende Information enthalten. Eine eventuelle Sättigung von zum Beispiel außerhalb des Durchstrahlungsbereichs eines Patienten liegenden Bildpunkten ist dagegen unbeachtlich.According to a development of the method, the further processing of the signals of read-out pixels takes place as a function of the sampling rate of the respective pixel. In particular, the signal gain can be adjusted according to the sampling rate. In this way, it can be taken into account that with conventional electronic image sensors, charge accumulation takes place in the pixels, which increases steadily with the exposure time. Rarer scanned pixels therefore contain a correspondingly higher charge accumulated over a longer period of time. The sensitivity of the readout devices is adjusted accordingly to this higher expected charge. It is important to ensure that in the less frequently read image areas, the sampling frequency is still high enough so that no saturation of the pixels occurs, which would result in a loss of information. This applies at least to those pixels which still contain information of interest. A possible saturation of, for example, outside the transmission range of a patient lying pixels is irrelevant.

Bei dem Bildsensor kann es sich insbesondere um einen solchen handeln, welcher für Röntgenstrahlen sensitiv ist. Solche Bildsensoren kommen bei medizinischen Bildgebungsverfahren wie zum Beispiel der Röntgen-Computertomographie zum Einsatz, wobei in den entsprechenden Anwendungen häufig eine zeitlich hoch aufgelöst Darstellung von räumlich begrenzten interessierenden Bereichen erforderlich ist. Die für medizinische Bildgebungsverfahren erforderlichen Gerätschaften sind in der Regel sehr kostenintensiv, so dass hier die optimale Ausnutzung vorhandener Ressourcen besonders vorteilhaft ist.In particular, the image sensor may be one that is sensitive to X-rays. Such image sensors are used in medical imaging methods such as, for example, X-ray computed tomography, wherein in the corresponding applications often a high-temporal representation of spatially limited areas of interest is required. The equipment required for medical imaging procedures are usually very costly, so that the optimal use of existing resources is particularly advantageous here.

Gemäß einer Weiterbildung des Verfahrens werden diejenigen Bildpunkten und/oder Bildpunktgruppen, die mit einer geringeren Abtastrate ausgelesen werden, mit einer geringeren Intensität bestrahlt. Die mit geringerer Abtastrate ausgelesenen Bildpunkte haben zwischen zwei Auslesetakten mehr Zeit zur Verfügung, um Bildinformation - zum Beispiel in Form von Ladung - anzusammeln. Diese Bildpunkte können somit mit einer geringeren Intensität der zur Bilderzeugung verwendeten Strahlung belichtet werden, ohne dass die bei der selteneren Abtastung der Bildpunkte zur Verfügung stehende Bildinformation hierdurch vermindert würde. Die somit gegebene Möglichkeit, Bildbereiche mit einer geringeren Intensität zu belichten, ist insbesondere bei medizinischen Röntgenabbildungen von Vorteil, denn in diesem Fall kann durch eine lokale Strahldämpfung die Dosis minimiert werden, welcher der Patient ausgesetzt ist.According to a development of the method, those pixels and / or pixel groups which are read out at a lower sampling rate are irradiated with a lower intensity. The pixels read out at a lower sampling rate have more time between two read-out clocks in order to accumulate image information, for example in the form of charge. These pixels can thus be exposed with a lower intensity of the radiation used for image generation, without the image information available in the case of the less frequent scanning of the pixels being reduced as a result. The thus given possibility of exposing image areas with a lower intensity is advantageous, in particular in the case of medical X-ray images, because in this case, the dose to which the patient is exposed can be minimized by a local beam attenuation.

Die Erfindung betrifft ferner eine Vorrichtung zum Auslesen eines in Bildpunkte unterteilten elektronischen Bildsensors, welche eine Adressierungseinheit zur Auswahl der in einem Takt auszulesenden Bildpunkte und/oder Bildpunktgruppen sowie eine Leseeinheit zum Auslesen der ausgewählten und adressierten Bildpunkte und/oder Bildpunktgruppen enthält. Dabei ist die Adressierungseinheit so eingerichtet, dass sie die adressierten Bildpunkte und/oder Bildpunktgruppen mit unterschiedlicher Rate auswählt. Anders als bei üblichen Adressierungseinheiten werden somit die in Frage kommenden Bildpunkte oder Bildpunktgruppen nicht in geordneter Reihenfolge mit gleicher Häufigkeit ausgewählt, sondern es gibt mindestens zwei Mengen von Bildpunkten oder Bildpunktgruppen, wobei die Elemente der einen Menge öfter von der Adressierungseinheit ausgewählt werden als die Elemente der anderen Menge.The invention further relates to a device for reading an electronic image sensor subdivided into pixels, which contains an addressing unit for selecting the pixels and / or pixel groups to be read out in one clock and a reading unit for reading the selected and addressed pixels and / or pixel groups. In this case, the addressing unit is set up such that it selects the addressed pixels and / or pixel groups at different rates. Unlike conventional addressing units, the pixels or pixel groups in question are thus not selected in the same order with the same frequency, but there are at least two sets of pixels or pixel groups, the elements of which are selected by the addressing unit more often than the elements of the different amount.

Mit einer derartigen Vorrichtung lässt sich das oben erläuterte Verfahren implementieren, so dass die dort geschilderten Vorteile erreicht werden können. Die Adressierungseinheit und die Leseeinheit der Vorrichtung können dabei insbesondere so ausgestaltet werden, dass sie auch die verschiedenen Varianten des Verfahrens realisieren können, also zum Beispiel eine zeilenweise Einteilung des Bildes, ineinandergreifende Bildpunkt-Mengen unterschiedlicher Abtastrate, eine Sensitivität des Bildsensors für Röntgenstrahlen und dergleichen.With such a device, the above-explained method can be implemented, so that the advantages described there can be achieved. In this case, the addressing unit and the reading unit of the device can in particular be designed such that they can also realize the various variants of the method, ie for example a line-by-line division of the image, intermeshing pixel quantities of different sampling rates, a sensitivity of the image sensor for X-rays and the like.

Insbesondere kann die Leseeinheit so eingerichtet sein, dass sie die Verarbeitung der ausgelesenen Signale der Bildpunkte nach der Rate ausrichtet, mit welcher die jeweiligen Bildpunkte und/oder Bildpunktgruppen adressiert wurden. Vorzugsweise wird die Signalverstärkung dieser Rate angepasst, so dass berücksichtigt werden kann, dass seltener abgetastete Bildpunkte eine aufgrund der längeren Belichtungszeit höhere Signalstärke erwarten lassen.In particular, the reading unit can be set up in such a way that it aligns the processing of the read-out signals of the pixels with the rate at which the respective pixels and / or pixel groups were addressed. Preferably, the signal gain is adjusted to this rate, so that it can be taken into account that less frequently sampled pixels expect a higher signal strength due to the longer exposure time.

Im Folgenden wird die Erfindung mit Hilfe der Figuren beispielhaft erläutert. Es zeigen:

Fig. 1
das Röntgenbild einer Hand mit einer Unterteilung des Bildes in Bereiche höheren und geringeren Interesses;
Fig. 2
die zeitliche Abstimmung der Ansteuerung der Röntgenröhre sowie des Auslesens der Bildpunkte bei einem erfindungsgemäßen Verfahren.
In the following, the invention will be explained by way of example with the aid of the figures. Show it:
Fig. 1
the X-ray image of a hand with a subdivision of the image into areas of higher and lower interest;
Fig. 2
the timing of the control of the X-ray tube and the reading out of the pixels in a method according to the invention.

Figur 1 zeigt das Röntgenbild 1 einer Hand, wobei im Zentrum des Bildes ein interessierender Bereich 2 (ROI) hervorgehoben ist. Der Rest 3 des Bildes stellt einen Bereich geringeren Interesses dar. Des weiteren sind am Rand des Bildes die Gate-Zeilen 5 des interessierenden Bereiches 2 sowie die Gate-Zeilen 6 des übrigen Bereiches 3 angedeutet, und am unteren Bildrand sind die Verstärkungschips 4 dargestellt, welche dem Auslesen von Bildzeilen dienen. FIG. 1 shows the X-ray image 1 of a hand, wherein in the center of the image, a region of interest 2 (ROI) is highlighted. The rest 3 of the image represents a region of lesser interest. Furthermore, the gate lines 5 of the region of interest 2 and the gate lines 6 of the remaining region 3 are indicated at the edge of the image, and the reinforcement chips 4 are shown at the lower edge of the image, which serve the reading out of picture lines.

Bei dem Bildsensor handelt es sich um einen FDXD-Detektor, der ausgelesen wird, indem Zeile für Zeile direkt zu einem Feldausgang übertragen wird. Dabei werden beim Auslesen einer Zeile keine Zeilen der Nachbarschaft betroffen. Anders als bei zum Beispiel CCD-basierten Bildgebern ist nicht jedesmal ein vollständiges Auslesen des Bildes erforderlich. Die nicht ausgelesenen Bildzeilen, die in einem bestimmten Takt bzw. Zyklus nicht adressiert wurden, bleiben dabei in der Regel für ihre weitere Verwendung unbeeinträchtigt. Dies gilt unter der Bedingung, dass während der mehrfachen Belichtung durch Röntgenimpulse kein relevantes Pixel eine Sättigung erreicht. Nicht relevante Pixel sind zum Beispiel solche, die dem direkten Strahl ohne Passage durch den Patienten ausgesetzt sind.The image sensor is an FDXD detector which is read out by transmitting line by line directly to a field output. It will be read out a line does not affect any lines of the neighborhood. Unlike CCD-based imagers, for example, complete readout of the image is not required every time. The non-read-out picture lines which were not addressed in a particular cycle or cycle, as a rule, remain unimpaired for their further use. This is true on condition that no relevant pixel reaches saturation during the multiple exposures by X-ray pulses. Non-relevant pixels are, for example, those exposed to the direct beam without passage through the patient.

Die in Figur 1 dargestellte zentrale ROI 2 wird durch Adressierung der entsprechenden Gate-Zeilen 5 mit einer erhöhten Abtastrate ausgelesen. Diese Abtastrate kann zum Beispiel 60 Bilder pro Sekunde betragen. Mit einer geringeren Rate von zum Beispiel der Hälfte oder einem Viertel der maximalen Abtastrate (das heißt 30 oder 15 Bilder pro Sekunde) wird dann das komplette Bild unter Verwendung aller Gate-Zeilen 5 und 6 entsprechend ihrer Reihenfolge ausgelesen. Die Sensitivität der Verstärkungschips 4 wird während des Auslesens entsprechend der Ladungsmenge umgeschaltet, die innerhalb und außerhalb der ROI 2 zu erwarten ist.In the FIG. 1 shown central ROI 2 is read out by addressing the corresponding gate lines 5 with an increased sampling rate. This sampling rate may be, for example, 60 frames per second. At a lower rate of, for example, one-half or one-quarter of the maximum sampling rate (ie, 30 or 15 frames per second), then the complete image is read using all the gate lines 5 and 6 according to their order. The sensitivity of the amplifying chips 4 is switched during readout according to the amount of charge expected inside and outside the ROI 2.

Figur 2 zeigt schematisch die Zeitabläufe verschiedener Vorgänge bei Durchführung des erfindungsgemäßen Verfahrens. Auf der horizontalen Achse ist dabei die Zeit aufgetragen. FIG. 2 schematically shows the time sequences of various processes in carrying out the method according to the invention. The time is plotted on the horizontal axis.

Das oberste Diagramm a) von Figur 2 zeigt die Belichtungsimpulse, welche von der Röntgenröhre abgegeben werden. Während jedes Impulses sammelt sich in den Bildpunkten des Bildsensors additiv eine entsprechende Ladungsmenge an, welche beim Auslesen des Bildpunktes abgeführt wird.The top diagram a) of FIG. 2 shows the exposure pulses emitted by the x-ray tube. During each pulse accumulates in the pixels of the image sensor additively a corresponding amount of charge, which is dissipated when reading the pixel.

Das zweite Diagramm b) von Figur 2 zeigt die Adressierung der Gate-Zeilen 5 und damit das Auslesen des interessierenden Bereiches 2 (ROI). Nach Beendigung des Auslesens kann ein neuer Röntgenimpuls gegeben werden. Da zwischen zwei solchen Röntgenimpulsen nicht das komplette Bild ausgelesen werden muss, kann ihr Abstand entsprechend kürzer gemacht werden, was zur verbesserten zeitlichen Auflösung der Darstellung des interessierenden Bereiches 2 führt.The second diagram b) of FIG. 2 shows the addressing of the gate lines 5 and thus the reading of the area of interest 2 (ROI). After completion of the readout, a new X-ray pulse can be given. Since the complete image does not have to be read out between two such X-ray pulses, their distance can be correspondingly shortened, which leads to the improved temporal resolution of the representation of the region of interest 2.

Im Diagramm c) ist die Adressierung der Gate-Zeilen 6 des Bereiches 3 außerhalb der ROI 2 dargestellt. Wie aus den Diagrammen b) und c) erkennbar ist, wird der interessierende Bereich ROI viermal ausgelesen, bevor einmal der übrige Bereich 3 des Bildes ausgelesen wird. Der interessierende Bereich ROI wird somit mit einer viermal höheren Abtastrate erfasst als der Rest des Bildes. In dem letzten in Figur 2 dargestellten Intervall zwischen zwei Röntgenimpulsen wird das vollständige Bild ausgelesen, also sowohl der interessierende Bereich ROI als auch der übrige Teil 3 des Bildes. Dementsprechend wird eine längere Zeit für das gesamte Auslesen benötigt, so dass das Intervall zwischen den zwei Röntgenimpulsen entsprechend größer zu wählen ist.In the diagram c) the addressing of the gate lines 6 of the area 3 outside the ROI 2 is shown. As can be seen from the diagrams b) and c), the region of interest ROI is read four times before the remaining area 3 of the image is read out once. The ROI of interest is thus detected at a four times higher sampling rate than the rest of the image. In the last in FIG. 2 the interval between two X-ray pulses is read out the complete image, ie both the region of interest ROI and the remaining part 3 of the image. Accordingly, a longer time is required for the entire readout, so that the interval between the two X-ray pulses is to be selected correspondingly larger.

Das unterste Diagramm d) aus Figur 2 zeigt die Sensitivität der Verstärker während des Auslesens. Zu erkennen ist, dass die Sensitivität während des Auslesens von Bildpunkten des interessierenden Bereiches ROI hoch und während des Auslesens des übrigen Bildbereiches 3 geringer ist. Diese Veränderung der Sensitivität berücksichtigt, dass die seltener ausgelesenen Bildbereiche 3 zwischen zwei Auslesevorgängen mehrfach belichtet wurden (nämlich im dargestellten Beispiel viermal), so dass sie eine entsprechend höhere Ladungsmenge erwarten lassen. Diese höhere Ladung wird durch die verringerte Sensitivität kompensiert.The lowest diagram d) off FIG. 2 shows the sensitivity of the amplifiers during readout. It can be seen that the sensitivity is high during the reading out of pixels of the region of interest ROI and lower during the reading out of the remaining image region 3. This change in sensitivity takes into account that the less frequently read image areas 3 were exposed several times between two reading processes (four times in the example shown), so that they allow a correspondingly higher charge quantity to be expected. This higher charge is compensated by the reduced sensitivity.

Das erfindungsgemäße Verfahren erlaubt es somit, den besonders interessierenden Bereich ROI eines Bildes mit höherer Abtastrate und daher zeitlich besser aufgelöst darzustellen. Weniger interessierende Bildbereiche werden zeitlich weniger stark aufgelöst, zeigen jedoch aufgrund der längeren Belichtung ein besseres Signal-zu-Rauschen Verhältnis.The method according to the invention thus makes it possible to represent the particularly interesting region ROI of a picture with a higher sampling rate and therefore in a better time-resolved manner. Less interesting image areas are less resolved in time, but show a better signal-to-noise ratio due to the longer exposure.

Claims (8)

  1. A method of reading out an electronic image sensor that is subdivided into picture elements,
    - from which electronic image sensor picture elements or groups of picture elements can be read out with a predetermined clock period, wherein
    - the image sensor is subdivided into at least two areas,
    - to which accordingly at least two quantities of picture elements or groups of picture elements are assigned,
    - the elements of which are read out at a different scanning rate,
    characterized in that
    - the area that is read out at a lower scanning rate exhibits a longer irradiation time;
    - the at least two areas are both used for image display; and
    - the quantities of picture elements and/or groups of picture elements are arranged so as to overlap at least in a sub-region of the picture area.
  2. A method as claimed in claim 1,
    characterized in that the picture elements are grouped so as to form lines of a two-dimensional image, and the lines that belong to a quantity are all read out at a uniform scanning rate.
  3. A method as claimed in claim 2,
    characterized in that the lines of picture elements of the image are alternately assigned to at least two quantities with different scanning rates.
  4. A method as claimed in at least one of the claims 1 to 3,
    characterized in that the further processing of the signals from picture elements read out, notably their amplification, is performed in dependence on the relevant scanning rate of the picture elements.
  5. A method as claimed in at least one of the claims 1 to 4,
    characterized in that the image sensor is sensitive to X-rays.
  6. A method as claimed in at least one of the claims 1 to 5,
    characterized in that the picture elements and/or the groups of picture elements that are read out at a lower scanning rate are irradiated with a lower intensity than those read out at a higher scanning rate.
  7. A device for reading out an electronic image sensor (1) that is subdivided into picture elements, which device is provided with an addressing unit for selecting the picture elements and/or groups of picture elements to be read out within one clock period as well as with a reading unit for reading out the selected and addressed picture elements and/or groups of picture elements,
    characterized in that
    the image sensor is subdivided into at least two areas, to which accordingly at least two quantities of picture elements or groups of picture elements are assigned, the addressing unit is arranged in such a manner that it selects the addressable picture elements and/or groups of picture elements at a different scanning rate, and the area selected at a lower scanning rate exhibits a longer irradiation time; wherein the at least two areas can both be used for image display, and the quantities of picture elements and/or groups of picture elements are arranged so as to overlap at least in a sub-region of the picture area.
  8. A device as claimed in claim 7,
    characterized in that the reading unit is arranged in such a manner that it adapts the processing, notably the signal amplification, to the scanning rate at which the relevant picture elements and/or groups of picture elements are addressed.
EP01125777A 2000-10-31 2001-10-29 Apparatus and method for reading out several sets of pixels with different sampling rates Expired - Lifetime EP1202561B1 (en)

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